Endoscopy instruments may be inserted into the body by introducing them into a cannula which has previously been inserted through the skin using a conventional trocar. A cannula is a thin, hollow tube with an open tip on the distal end and a hub of expanded diameter on the proximal end. The hub acts as a guide for directing an instrument or a trocar into the lumen of the tube portion of the cannula. A trocar is an instrument whose sharpened tip projects a short distance beyond the distal end of a surrounding cannula tube. The cannula and the trocar form a small puncture wound in the body as they are inserted through the body tissue. The trocar is then removed leaving the cannula in position with its distal end located in a desired position in the body and with its proximal hub extending outside the body. Thus, the cannula provides an entry site for various endoscopy instruments into the body. A variety of surgical tools and appliances can be inserted through a cannula, for instance a surgical cutting instrument, an aspiration or irrigation tube, or various optical or fiberoptic viewing devices, for example, telescopes which permit the surgeon to inspect the interior of the body.
Particularly with viewing instruments, like telescopes, it is important that the orientation of the optical system inside the body be readily observable from outside the body. Very often the tip of the telescope is designed to look at an angle to its axis rather than straight ahead. The distal end of the telescope is placed at the distal end of the insertion cannula tube so that the telescope will be protected during use by the surrounding tip of the cannula tube, which is usually made of metal or a relatively hard plastic. The distal tip of the cannula tube is also cut at an angle corresponding to the angle of the telescope to permit side viewing. When this side viewing configuration is contemplated, it is important to have the telescope in proper rotational registration with the distal end of the cannula tube. Otherwise, the telescope will focus on the confronting surface of the protective cannula tube rather than at the body structures. It is, thus, important that the precise axial position of the end of the telescope and its rotational orientation be known and controllable.
It is also important to orient the telescope properly with respect to any light source that is inserted into the body so as to reduce glare and shadows.
It is also important in the operating room environment that the telescope or other endoscopy instrument can be easily inserted through the cannula and locked into position so that the surgeon will not have to spend valuable operating time adjusting and aligning the telescope or other instrument.
It is also desirable to have tight sealing engagement between the cannula assembly and the endoscopy instrument to permit irrigation or aspiration of fluid with respect to the operative site. It would be desirable to have an insertion cannula with a locking mechanism which would allow the surgeon to insert a endoscopic instrument, for example a telescope, quickly and easily and be assured that the telescope is in its proper rotational and axial position and that that position could be maintained without constant monitoring and adjusting.